Process for protecting a metallic surface against corrosion and wear

ABSTRACT

Metallic articles comprising at least one Group IB element, for example articles made of copper and copper alloys, are protected against corrosion and wera by forming on the surface thereof, by chemical vapour deposition, a layer of amorphous and transparent aluminium oxide. The layer can be formed by pyrolysis of a volatile aluminium compound such as aluminium chloride.

United States Patent 1191 Schachner et a1.

1451 May 20, 1975 PROCESS FOR PROTECTING A METALLIC SURFACE AGAINST CORROSION AND WEAR Inventors: Herbert Schachner; Helmut Tannenberger; Bastian O. Baumberger, all of Geneva, Switzerland Battelle Memorial Institute, Carouge, Geneva, Switzerland Filed: June 17, 1974 Appl. No.: 480,152

Assignee:

Foreign Application Priority Data June 15, 1973 Switzerland 8705/73 US. Cl 427/226; 427/248 Int. Cl. C23c 11/08 Field of Search 117/106 R, 129, 127, 230;

References Cited UNITED STATES PATENTS 10/1944 Getz et a1. 117/129 X Wheildon 117/129 X 3,290,233 12/1966 Hay et al. 117/230 X 3,510,343 5/1970 Twells 117/129 X 3,836,392 9/1974 Lux et a1 ll7/l06 R X Primary Examiner-Leon D. Rosdol Assistant Examiner-Harris A. Pitlick Attorney, Agent, or Firm-Karl E. Ross; Herbert Dubno 5 Claims, No Drawings PROCESS FOR PROTECTING A METALLIC SURFACE AGAINST CORROSION AND WEAR BACKGROUND OF THE INVENTION Even today, cocks and valves are generally made of copper or a copper alloy, such as brass. Formerly these articles had been unprotected which involve frequent manual maintenance in order to maintain their surface brightness and to remove the scratches and marks brought about by wear. The brassware had to be polished by means of light abrasives. This was a disadvantage that has now been eliminated by the technique of coating surfaces with a layer of a hard metal more resistant to corrosion, especially nickel and, subsequently, chromium. Coatings of this kind, which even today are still commonplace, are applied by electrochemical deposition, in particular by electroplating. Although they are satisfactory in regard to their protective effect, they do have the disadvantage of necessitating one or more relatively delicate treatments of the machined articles in baths of which some are toxic and require skilled personnel, resulting in an increase in price in relation to unprotected articles. In addition, coatings of this kind have eliminated the appearance of the basic material, namely, copper, brass or any other copper alloy. This accounts for the advantage there would be in any method of protection which, without in any way losing its effectiveness, would leave the appearance of the underlying metal intact, i.e., would cover the underlying metal with a transparent protective layer.

In the case of clocks and watches, especially watch cases or items of jewelry, it is their character of luxury articles which has resulted in their being made of noble metals, such as platinum, gold, silver. However, even these metals are subject to wear and corrosion, albeit to varying degrees, so that, in their case too, a method of protection based on the application of a protective layer would be of advantage to an extent which would be even greater if this protective layer were to be transparent, so as to maintain the allure in the brilliance of the precious metal of which the article (if it is a solid article) or at least its surface (gold-plated or silverplated articles) is made. In order to popularise clocks and watches, especially watches, attempts have been made to make the cases of metals that are cheaper than the precious metals referred to above. Since ordinary steel cannot seriously be taken into consideration on account of its sensitivity to corrosion, attention has been directed to stainless steel. However, stainless steel has a very cold visual appearance which emanates from the slightly bluish colour which it assumes when polished. It is for this reason that attempts have been made to use other alloys with a warmer appearance to make the cases for medium-priced and low-priced watches. However, these alloys, generally copper alloys such as the alloy Cu Ni Mn (20%), are prone to corrosion and, due to their average hardness, to wear as well, which is reflected in their tendency to scratch and tarnish in use. Accordingly, cases of this type have to be subjected to surface treatment(s) designed to protect them against corrosion (i.e., chemical protection) against wear (i.e., mechanical protection) or against both. The various known treatments which are applied even today are, for the most part, electroplating treatments which cover the surface of the cases with a protective layer obtained electrochemically.

However, this protective layer changes the surface appearance of the underlying metal.

In one known process, described in French Patent Application No. 2,1 10,202, a protective layer is deposited by the technique of chemical vapour deposition rather than by electrochemical treatment. However, this process can only be used for articles made of steel, and is not suitable for metals of Group [B of the Periodic System or their alloys. In addition, the protective substances used in this process apparently do not form a transparent layer.

It is an object of the present invention to protect metallic surfaces comprising at least one Group IB element with a protective layer which is both hard wearing and transparent.

SUMMARY OF THE INVENTION The present invention, which is concerned with protecting articles whose surface at least is made of a metal of Group IB or of an alloy containing at least one metal of this group, especially the alloy Cu-Ni (20%)-Mn (20), relates to a process which is distinguished by the fact that the surface of this article is coated with a layer of amorphous, transparent aluminium oxide obtained by chemical vapour deposition.

The protective layer is made of amorphous alumina A1 0 In the context of the invention, the word amorphous means that the Xray diffractogram of this layer does not show the known lines which characterise the various well-crystallised forms of alumina A1 0 In addition, this layer is transparent so that the appearance of the underlying metal is in no way affected.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of the invention is intended in particular for articles of small dimensions whose surface is re? quired to retain a durable, attractive and aesthetic appearance despite frequent handling, or to have a long service life. This is the case, for example, with cocks and valves so far as the first category is concerned, and with clocks and watches especially watch cases, even jewellery, so far as the second category is concerned.

The process according to the invention comprises using the technique of chemical vapour deposition to obtain the formation, over the surface of the article, of an adherent, transparent layer of amorphous alumina A1 0 which, by virtue of its chemical inertia and its physical hardness, provides the required protection. To this end, a volatile compound of aluminium, for example aluminium chloride AlCl is preferably subjected to hydrolysis under heat (pyrohydrolysis) in the presence of steam. For this purpose, the article to be treated is placed in a chamber in which the air has been replaced by an inert gas (hydrogen H or argon A). The pressure in this chamber is reduced to a value between 0.1 and Torr, after which the article is heated to a temperature in the range from 300 to 800C either by placing the chamber itself in a radiation furnace or by subjecting the article to highfrequency induction heating, whilst at the same time passing through the chamber a gas mixture of a selected volatile aluminium compound and steam, each of these components being introduced by a so-called carrier gas with which it is mixed before being introduced into the chamber. The carrier gas has to be inert.

3 It is preferred to use hydrogen H or a rare gas, such as argon A.

The principal working conditions are illustrated by the following Examples.

EXAMPLE 1 EXAMPLE [1 Article of Cu-Ni (20%)-Mn (20%) alloy Temperature: 600C Pressure in the chamber: 4 Torr Active components and carrier gases:

1. AlCl input 30 mg .mn' H input 600 co rnn" 2. H O, input 6 mg inn H input 600 cc mn Reaction time: 12 minutes Average thickness of the protective Al O layer: 3

,um Knopp micro hardness: 1,200 kg mn' EXAMPLE 111 Article of silver Ag Temperature: 650C Pressure in chamber: Torr Active components and carrier gases:

4 l. AlCl input 10 mg rnn' H input 200 cc mn" 2. H O, input 2 mg mn H input 200 cc-,,,,,,

Reaction time: 10 minutes Average thickness of the protective A1 0 layer: 2

In each of these Examples, the protective A1 0 layer was perfectly transparent and in no way affected the appearance of the underlying metal. Resistance to corrosion was excellent. In particular, there was no evidence of corrosion after exposure for 24 hours to an atmosphere containing ammonia gas NH;,.

The above Examples relate to the case where chemical vapour deposition is based on hydrolysis. However, deposition can be carried out by other reactions, in particular by the pyrolysis of an alkoxide, such as aluminium isopropylate (Al(C H-,O)

We claim:

1. A process for protecting against corrosion and wear a metallic surface consisting essentially of at least one element belonging to Group IB of the Periodic Classification of Elements in pure or alloyed form, which process comprises forming on said surface by chemical vapor deposition a layer of amorphous and transparent aluminium oxide.

2. A process as claimed in claim 1, wherein said chemical vapor deposition is carried out by the pyrohydrolysis of a volatile aluminium compound.

3. A process as claimed in claim 2, wherein said volatile aluminium compound is a halide.

4. A process as claimed in claim 3, wherein said hal ide is aluminium chloride, and wherein said pyrohydrolysis is carried out at a temperature in the range from 300 to 800C and at a pressure of from 1 Torr to Torr.

5. A process as claimed in claim 1, wherein said surface is made of a copper alloy containing nickel and manganese.

Dedication 3,885,063.Herbert Schachner; Helmut T annenberger; Bastian O. Baumberger, Ge-

neva, Switzerland. PROCESS FOR PROTECTING A METTALLIC SURFACE AGAINST CORROSION AND WEAR. Patent dated May 20, 1975. Dedication filed Mar. 26, 1984, by the assignee, Battelle Memorial Institute.

Hereby dedicates to the People of the United States the entire remaining term of said patent.

[Oflicial Gazette July 3, 1984.] 

1. A PROCESS FOR PROTECTING AGAINST CORROSION AND WEAR A METALLIC SURFACE CONSISTING ESSENTIALLY OF AT LEAST ONE ELEMENT BELONGING TO GROUP IB OF THE PERODIC CLASSIFICATION OF ELEMENTS IN PURE OR ALLOYED FORM, WHICH PROCESS COMPRISES FORMING ON SAID SURFACE BY CHEMICAL VAPOR DEPOSITION A LAYER OF AMORPHOUS AND TRANSPARENT ALUMINIUM OXIDE.
 2. A process as claimed in claim 1, wherein said chemical vapor deposition is carried out by the pyrohydrolysis of a volatile aluminium compound.
 3. A process as claimed in claim 2, wherein said volatile aluminium compound is a halide.
 4. A process as claimed in claim 3, wherein said halide is aluminium chloride, and wherein said pyrohydrolysis is carried out at a temperature in the range from 300* to 800*C and at a pressure of from 1 Torr to 100 Torr.
 5. A process as claimed in claim 1, wherein said surface is made of a copper alloy containing nickel and manganese. 